Method of keying radio transmitters



March 7, 1939. c. w. HANsELl. E14-AL' 2,149,437

` METHOD oF KEYING RADIO TRANSMITTERS Filel Feb. 26, 1958 .NQ WS ik H l IIIH nNlvEN-rolasv l ME. GOLDST/NE BYau/H L manga Patented Mer. 7, 1939 PATENT OFI-'ica IIETHOD F KEYIN'G RADIO TRANSMITTERS Clarence W. Hansell and Hallan E. Goldstne,

Port Jefferson, N. Y., -assig-nors to Radio Corporation of America, a corporation of Delaware Application February 26.1938, serial No. 19z,esz f 1o claims. (ci. ris-6s) This invention relates to the art of keying radio transmitters and discloses a novel method and means whereby the keying can be accomplished in a manner that will have the advantages of extremely high speed keying and -can be used `on fairly high power tubes without requiring a large amount ofpower to be dissipated in the absorbers or keying tubes. Keying speed is Vincreased and emciency improved in accordance with our invention by keying the grid of an amplier tube the cathode of which is in the nonkeyed state positive .relative to the grid (also positive) suicient to cause cut-oil?. tube may be of smaller than normal rating and l5 preferably is of a size `such that with proper direct current connections., between it and the direct current source andthe grid of the amplifier tube, 'the anode direct current of the keying tube when conductive is substantially equal to the maximum grid current of the amplifying tube. Maintaining the grid positive permits the co-relation between the plate current o1 the keying tube and the grid current of the amplier tube described above, and permits increased keying speeds to be kobtained with reduction of lost or dissipated current in keying. The balancing ofthe keying tube current against the keyed circuit current improves the stability o1' the oscillator voltage and consequently its frequency of operation is improved. An additional feature which further increases the speed, eiciency and smoothness of operation is the use of non-linear resistance in the cathode returns of the oscillator, buffer amplifier and power amplifier. The oscillator cathode oats above ground due to the potential drop in thev non-linear resistance and its grid being connected to its cathode by a selfbiasing resistance it operates at constant bias and `generates waves of constant frequency.

Since the oscillator operates continuously thisv non-linear resistance produces a iixed bias for all of the tubes of the system. Moreover, the plate currents of the buier amplier and power ampliiier are keyed between cut-ofi and full cur- 4 rent and but for the action of the said non-linear resistances this would put a large variable voltage on the oscillator plate and consequently cause changes in the continuous Ywave frequency.

The present invention and in particular the features mentioned above and the .specication which follows, are applicable to all radio transmitters and in particular to radio transmitters,

where high speeds such vas facsimile are to be adequately handled. 'This new system which 'I'he keying produces the desired important.

In describing our invention more in detail rei.'- erence will be made to the attached drawing wherein the single gure illustrates our novell 5 means including `the keyed buier ampliiier with results is therefore :very

the cathode at high positive potential, the circuit for balancing the grid current of the keyed tube against the current of the keying tube and the non-linear resistances. 1o

By referring to the ilgure the details o1' operation can be more clearly described. A radio firequency amplifying tube I has its anode 8 connected to the positive-terminal of a direct current source and its cathode 9 connected to the 16 negative terminal of said sourcethrough Thyrite resistances so that the iilament circuit I0 is maintained at a positive potential with respect to-said negative'terminal vand ground. The grid I2 of this tube is connected to its radio frequency 20 driving circuit 3 and from there is connected through suitable resistances 4 and `5 back to the positive terminal of the anode potential source. A keying tube 2 has its anode I4 connected to 4 and its cathode grounded so that it will draw 25 current through resistor 4 when its grid is maintained at zero potential and will draw no current through resistor 4 when its grid is biased negative a substantial amount. Keying potentials from any source I6 are applied to the vgrid 30 I8 of tube. 2 to key the same so that tube 2 is alternately more conductive andless conductive. The source of continuous wave energy 20 may be coupled to 3 at 22 and may comprise a tube generator with its anode 24' connected to 35 v the source of direct current and its cathode 26- connected to the Thyrite resistance 29. The keyed wave energy is supplied from the anode. 8 of tube I to a tuned circuit 28 and induced therefrom on 30 vand the grids of a power amnli- 40 ner tubes, the cathodes o1' which are also connected to the Thyrite resistance 29 as shown. The anodes of the power amplier tubes are connected to .the direct current source.

'In' operation, the key is closed on the negative 45 potential terminaland the grid of tube 2 is held 200 v. negative. Tube 2 draws little orno current through resistor 4. However, current ows through 4 to the grid of I and the potential drop through 4 is such that a. relatively high positive 56 potential is applied to the grid I2 of tube I.l This potential is suiliciently near to the potential of the cathode 9 to make the tube I conductive so that wave energy is amplified and supplied vto the power ampliiier. The tube I is now conduc- 55 tive and due to the radio frequency drive impressed on its grid circuit 3 the grid will draw sufiicient grid current to maintain this tube at a proper operating point. Now, if tube 2-is 5 made conductive by reducing its grid voltage to zero the tube 2 will draw sufiicient anode current through resistor 4 to bias tube I to cut-olf. For example. if we assume the grid of tube I around 200 or 400 volts positive since tube I filament is 2000 v. positive with respect to ground and its grid being, say, 400 v. positive, the grid therefore is 1600 v. negative with respectto the filament and the tube will be cut offA at the peaks of the radio frequency voltage and will not override the 1600 v.'bias. Since tube I is now cut off no wave energy is amplied therein and supplied to the power ampliiler and the system is 'on Space. 'I'he values given above are for illustration only and the scope of the invention should not be limited by these gures. By adjusting the values of resistor 5 and' resistor a condition can be maintained where the grid circuit of tube I draws the same amount of currentwhen it is conducting as the anode circuit of tube 2 willdraw when it is conducting and tube I is cut oil?. This means that there is essentially no change in vplate current. through resistor 4 between key down and key up condition or mark and space. The time constant of this keying system is quite small due to the fact that the capacities in the circuit are relatively small, thus permitting lngh speed keying.

Another feature of this particular keying scheme is that Thyrite is used in the cathode return circuit of the tubes to obtain their bias. The oscillator tube in 20 runs continuously since it is not keyed and furnishes the xed bias by means of the Thyrite 29 in its cathode circuit 40 for the other tubes. Only one rectier is used to supply the plate voltage to the transmitter, thus eliminating the bias rectier and the other lower voltage plate supply rectier. The Thyrite resistors have a characteristic such that the potentlal drop therethrough does not increase linearly with respect to currentincreasev therethrough. Thus, switching of the buffer amplifier l tube and power tube irom little or no current to full current has .less eilect on the potential of the common source and consequently less effect on the frequency oi operation of the oscillator whichdraws its current from said source.

` We claim:

1. In atelegraphy system, a wave energy am- 65 plifier having an electrode excited by continuous wave energy to be keyed and an output electrode coupled with a utilization circuit, a keying tube having an electrode connected with means for impressing thereon potentials of diierent value to render said keying tube alternately more conductive and less conductive, said keying tubev having an anode and a cathode, direct current circuits interconnecting the anode and cathode of said keying tube with an electrode in said wave amplier to bias said tubes to potentials such that when the keying tube is more conductive the amplifying tube is less conductive and vice versa, and means in said direct current circuits for limiting the current flow to said last named electrode in said wave amplier tube when conductive to a value substantially equal to the anode current ilowing in said keying tube when it is conductive,

2. In a telegraphy system, a wave energy am- -plier having a control 'grid excited by continuousggaveenergy to be keyed and an output elecv trode coupled with a utilization circuit, a keying tube having a control grid connected with means for impressing thereon potentials of different value to render said keying tube alternately conductive and non-conductive, said keying tube 5 having an anode and a cathode, direct current circuits interconnecting the anode and cathode of said keying tube with the control grid of said continuous wave amplifier to bias said electrodes .values such that when the keying tube is con- 10 ductive the amplifying tube is non-conductivev and vice versa, and means in said direct current circuits for limiting the current flow to said control grid electrode in said continuous wave amplifier tube when conductive to a value substan- 15 tially equal to the anode current flowing in said keying tube when it is conductive.

3. In a telegraphy system, a keying tube having a control electrode, a cathode and an auxiliary electrode, an amplier having a control elec- 20 trode, a cathode and an auxiliary electrode, means for maintaining the cathode of said amplier positive with respect to the control velectrode of said amplier and the cathode of said keying tube, a source of direct current potential, 25 a direct current circuit interconnecting said source of direct current potential and the auxiliary electrode of said keying tube with the con-r trol electrode and cathode of said amplifier tube,

a current limiting impedance in the control elec- 30 trode to cathode circuit of said amplifying tube of such a value that maximum current flowing in said circuit is substantially equal to normal auxiliary electrode to cathode current in said keying tube, means for impressing continuous 35 wave energy on the control grid of said amplifying tube and means for varying the potential of the control grid of said keying tube between two values which alternately render said keying tube more conductive and less Lconductive to control 40 the direct current potential on-the control electrode of said amplier tube.

4. In a telegraphy system, a keying tube havinga control grid, a cathode and an anode, an

amplifier having a control grid, a cathode and 5 an anode, means for maintaining the cathode of said amplier positive with respect to ground, means for maintaining the control grid of said amplier positive with respect to ground, a source of direct current potential, a direct currentcir- 50 cuit interconnecting said source of direct current l potential and the anode and cathode of said keying tube with the control grid and cathode of said amplier tube, an impedance in the anode-tocathode circuit of said keying tube, means for 55 impressing continuous wave energy on the control grid of said amplifying tube and means for varying the potential of the control grid of said keying tube between two values to vary the conductivity of said keying tube, andthe variations 60 l oi potential drop in said impedance to vary the potential .of said amplifier control grid relative to its cathode.

5. In a telegraphy system, a keying tube having a control electrode. a cathode, an auxiliary 35 electrode. an amplier having a control electrode and a cathode, means for maintaining the cathode of said ampliiier highly positive with Vrespect to ground, means for maintaining the control electrode of said buffer amplier positive relative 70 to ground, a source of direct current potential, a direct current circuit including an impedance connecting said source of direct current potential and the auxiliary electrode and cathode of said keying tube, a connection between a point on 75 rent in the grid circuit of said amplier tube-such that a maximum it issubstantially equal to the amasar control grid, cathode and amplifier and a, power` cuit is substantially equal to normal auxiliary.

electrode-to-cathode current in said keying tube,

means for impressing continuous wave energy on the'control grid of said .amplifying tube and means for varying the potential oi the control electrode of said keying tube between two values which alternately render said keying tube conductive 'and non-conductive.

6..In a telegraphy system, an ampliiler tube having a cathode and a control grid, means for impressing wave energy to be keyed continuously on the control grid and cathode of saidamplier tube, a source of direct current'.y potential,v nonlinear resistance means connecting the anode and cathode impedances oi said ampliiier to said source of direct current potential, a keying tube having a control grid, a cathode and an anode, direct current circuits interconnecting the anode and cathode of said keying tube and the control grid and cathode of said amplier tube withv said source of direct current potential, means in said last named circuits to limit the iiow oi.' direct curdirect current iiowing in the anode and cathode of said keying tube, and means for keying the potential on the control grid of said keying tubes between values at which it is alternately conductive and non-conductive.

'1. In a telegraphy system, an amplier tube having an anode, a cathode and a control grid. means for impressing continuous wave energy to be keyed .onthe control grid and cathode oi said amplier tube, a source of direct current potential, a power' ampliiier of the discharge tube type having an inputcoupled to said iirst -ampliiier .anode and an output coupled to a utilization circuit, non-linear resistance means connecting the anode and cathode impedances oi' said power ampliiier device and said ampliner to said source of direct current, a keying tube having a control grid', a cathode and ananode, direct current cir'- cuits .interconnecting the anode and. cathode off,

said keying tube and the control grid andcaihode oi' said amplier tube with said source of direct current potential, means in said last named v circuits to limit the iiow oi direct current -in the grid circuit oi said ampiier- -tube so that at maximum it is substantially equal to the di rect current dowingbetween the anode and cathode-0i said keying tube, andrneans for keying the potential on the controlgrldoi. said keying tubes between values at which s. m a telegram inwingacontrolgrid,acathoieandananodaa.4 `imiter amplifying tube havingfa control grid,

itl Vccnductive and non-conductive". f '1 amplifier tube having a control grid, cathode and anode, high frequency circuits coupling electrodes in said cscillatorv tube to the control grid of said bader amplifier tube and the anode of said buffer amplier tube to the control grid of said` power amplier tube, a source of direct current potential, a non-linear resistor, means including portions of said non-linear resistance connecting the cathodes of all of said tubes to the negative terminal of said source of direct current potential, connections between the anodes of all of said tubes and the positive terminal of said source of direct current potential, an impedance in the connection between the anode ot said keying tube and said `positive terminal, an impedance connecting the anode of said keying tube to the control grid of said buiier ampliiier tube and a source of keying potentials connected/betweenv the control grid and cathode oi' said keying tube.

v9. In -a telegraphy system, a source of direct current, a -source of continuous wave energy to be keyed comprising an electron discharge tube having electrodes connected in .alternating current circuits and in a direct current circuit including a non-linear resistance in series with said source of direct current. an amplifier tube hav-y ing a cathode connected to a point onsaid nonlinear resistance positive relative to ground or equivalent potential and an anode connected to said direct current source whereby said cathode is maintained at a substantially ilxed potential relative to .ground due to the continuous operation oi saiddlscharge tube, means for impressing wave energy from said discharge tube on saidampliiiertube, and means for controlling the conductivity oi said ampliilertube at signal irequency.

10. In a telegraphy system, a source of direct current. a source of continuous wave energy to be keyed comprising an electron discharge tube having electrodes connected in alternatingcurrent circuits and in a direct current circuit in-v -ot said discharge tube, means for impressing wave energy Ifrom said discharge tube on said amplifier tube, a keying tube having ananode v' direct current circuit including an impedance interconnecting an electrode in said amplider with said source oi direct current,l and means for varying the conductivity of said keying tube at signal frequency. 

